1. Field of the Invention
The present invention relates to methods for manufacturing inflatable bladders and also to inflatable bladders and footwear and other articles of manufacture which include such inflatable bladders.
2. Background Art
Inflatable articles of manufacture or bladders for use in inflatable articles of manufacture have been known for decades. Such articles of manufacture include inflatable air mattresses and pillows, inflatable life preservers and rafts, and athletic equipment. In the field of athletic equipment, inflatable bladders have been incorporated in the interior of balls (e.g., basketballs, footballs, soccer balls, etc.), as well as in apparel and protective equipment such as baseball and boxing gloves, helmets, chest protectors and footwear. When utilized in footwear, an inflatable bladder may be used to provide customized cushioning to the wearer's foot and to enhance fit. In some instances, an inflatable bladder may take the place of a lacing system to secure the shoe to the foot of the wearer. Inflatable bladders may also be used in the sole of a shoe to provide cushioning to the bottom of the wearer's foot and to absorb impact forces from walking, running and jumping.
U.S. Pat. No. 7,278,445 discloses a Shoe Having an Inflatable Bladder, the disclosure of which is incorporated herein by reference in its entirety.
U.S. Pat. No. 5,113,599 to Cohen et al. (the '599 patent) discloses an athletic shoe having an inflatable bladder. This patent discloses a variety of inflatable bladder configurations for use in the tongue, on lateral and medial sides, around the ankles, beneath the foot, or in the entirety of the shoe. The bladder of the patent is formed from a first thermoplastic urethane (TPU) film and a co-extensive second TPU film. The first and second films are attached to each other along pre-defined weld or pattern lines. A peripheral weld line of the bladder creates a sealed bladder compartment or chamber and prevents air from escaping from the bladder. The first and second films are further attached to each other at a number of circular points or interior weld lines to control the thickness of the bladder to prevent undesired “bulging”, which could cause discomfort to the wearer or inhibit proper fit.
The first and second films of the bladder of the '599 patent are welded together using radio frequency (RF) or dielectric welding. RF or dielectric welding uses high frequency radio energy to agitate the molecules of thermoplastic materials to a point where they melt and weld together to form a strong bond. To weld the bladder of the '599 patent, the coextensive films are placed between a brass die (having raised areas representing the desired peripheral, circular and interior weld lines) and a platten on an RF machine. After bringing the brass die and RF platten into contact with each other, the RF machine is activated and the first and second films are bonded to each other only at the raised areas on the brass die to form the peripheral, circular and interior weld lines. Upon completion of the welding step, the inflatable bladder is die-cut from the remainder of the coextensive first and second films and assembled into the shoe as appropriate by adhesives, conventional stitching or other fastening means. The first and second films of the '599 patent may also be adhered to each other by conventionally heated and appropriately patterned brass dies or by application of chemical adhesives or bonding agents suitable for use with thermoplastic films.
The patent further discloses inflation of the bladder by a pump permanently affixed to the bladder using the RF welding technique described above or any other sealing method appropriate for use with the films thereof. Alternatively, the bladder may be inflated by an off-board pump connectable to an inflation/deflation valve, also affixed to the bladder in a location easily accessed by the wearer. Other pumps and valves, suitable for use with inflatable bladders for footwear, are disclosed in U.S. Pat. Nos. 5,074,765 and 5,144,708.
While manufacture of an inflatable bladder using RF welding requires no adhesives or additional materials and has the advantages of precise patterning, decreased heat-degradation in areas of the film adjacent to weld lines and strength of seal, it is costly and time consuming to machine or chemically etch the brass dies for the inflatable bladder patterns, particularly where an article of manufacture is produced in a large range of sizes and in multiple configurations. Conventionally heated brass dies are also expensive to machine, while chemical adhesion is messy and requires cure time in controlled environments. Moreover, RF welding techniques are extremely sensitive, require that the films be sufficiently thick to prevent excessive melting of the film (which could cause a breach of the bladder), and often result in finished bladders that “curl” along their edges (which can complicate their assembly into articles of manufacture such as footwear).
Thus, it is desirable to provide a method for manufacturing inflatable bladders for use in footwear and other articles which is relatively inexpensive, time efficient and allows for the manufacture of a variety of bladder configurations and sizes, utilizing a process and materials resulting in little to no interruption or delay in the manufacturing process.